1. Field of the Invention
The present inventions relates to a boat propulsion system, and more specifically to a boat propulsion system including an engine.
2. Description of the Related Art
A boat propulsion unit including an engine is conventionally known (see JP-A-Hei 9-263294, for example). JP-A-Hei 9-263294 discloses a boat propulsion unit including an engine and a power transmission mechanism for transmitting a driving force of the engine to a propeller at a certain fixed speed reduction ratio. In the boat propulsion unit, the driving force of the engine is directly transmitted to the propeller via the power transmission mechanism so that the propeller speed increases in proportion to the engine speed as the engine speed increases.
However, the boat propulsion unit (boat propulsion system) disclosed in JP-A-Hei 9-263294 has a disadvantage in that it is difficult to improve the acceleration performance at a low speed in the case where the speed reduction ratio of the power transmission mechanism is set so as to increase the maximum speed. In contrast, in the case where the speed reduction ratio of the power transmission mechanism is set so as to improve the acceleration performance at low speed, it is disadvantageously difficult to increase the maximum speed. That is, the boat propulsion unit disclosed in JP-A-Hei 9-263294 has a problem in that it is difficult to achieve both the acceleration performance and the maximum speed desired by a user.